The chapters assembled in this volume deal with preferential trade agreements (PTAs), a topic that has repeatedly attracted the interest of analysts. One might naturally wonder why we need to revisit this issue once again. We believe that there are various good reasons, not necessarily mutually coherent. First, from a pure policy perspective, it is the World Trade Organization (WTO) through its Director General that has placed this item among the priority items for (re)negotiation. Obviously, the feeling must be that something has not been functioning as expected. We want to explore the legitimacy of this claim. On the other hand, recent empirical research casts doubt to the old “trade diversion” school: papers have seen the light of day arguing that no (or insignificant) trade diversion has resulted from the formation of recent PTAs. If so, why should we deal with PTAs at all? Then there is the issue of content of PTAs: many recent PTAs (i.e., after the advent of theWTO) have a subject matter that does not come under the mandate of the WTO as we now know it. The obvious question in this context is what the role should be of the WTO when dealing with issues such as environmental protection ormacroeconomic cooperation.